1. Field of the Invention
The present invention relates to a phase-change memory device. More particularly, the present invention relates to an upper electrode in a chalcogenide memory cell. In particular, the present invention relates to a damascene structure select line in a phase-change memory cell structure.
2. Description of Related Art
Typical memory applications include dynamic random access memory (DRAM), static random access memory (SRAM), erasable programmable read only memory (EPROM), and electrically erasable programmable read only memory (EEPROM).
Solid state memory devices typically employ micro-electronic circuit elements for each memory bit (e.g., one to four transistors per bit) in memory applications. Since one or more electronic circuit elements are required for each memory bit, these devices may consume considerable chip xe2x80x9creal estatexe2x80x9d to store a bit of information, which limits the density of a memory chip. The primary xe2x80x9cnon-volatilexe2x80x9d memory element of these devices, such as an EEPROM, typically employ a floating gate field effect transistor device that has limited re-programmability and which holds a charge on the gate of field effect transistor to store each memory bit. These classes of memory devices are also relatively slow to program.
Phase change memory devices use phase change materials, i.e., materials that can be electrically switched between a generally amorphous and a generally crystalline state, for electronic memory application. One type of memory element originally developed by Energy Conversion Devices, Inc. of Troy, Mich. utilizes a phase change material that can be, in one application, electrically switched between a structural state of generally amorphous and generally crystalline local order or between different detectable states of local order across the entire spectrum between completely amorphous and completely crystalline states. Typical materials suitable for such application include those utilizing various chalcogenide elements. These electrical memory devices typically do not use field effect transistor devices, but comprise, in the electrical context, a monolithic body of thin film chalcogenide material. As a result, very little chip real estate is required to store a bit of information, thereby providing for inherently high density memory chips. The state change materials are also truly non-volatile in that, when set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that value is retained until reset as that value represents a physical state of the material (e.g., crystalline or amorphous). Thus, phase change memory materials represent a significant improvement in non-volatile memory.
One aspect of fabrication deals with the complexity of the chalcogenide material. Because of its unusual behavior in the semiconductor processing regime, measures must be taken to avoid creating a fugitive material during routine thermal processes. Additionally, because it is more chemically reactive than several conventional materials used in the semiconductor processing regime, damage to the chalcogenide material is likely. Other measures must be taken to facilitate the patterning of the memory material.